1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a metallic bellows contained in, for example, an accumulator.
2. Description of the Related Art
Some of apparatuses whose housing contains a liquid and a compressed gas, such as accumulators, may use a metallic bellows for dividing the liquid and the gas. Conventionally, there have been proposed forming apparatuses for manufacturing bellows of this type. In one such conventional apparatus, split dies as many as pleats of the bellows to be formed are arranged between a stationary-side holder and a movable-side holder. These dies and the movable-side holder are movable along guide means. Return springs are disposed compressed between each two adjacent dies so that the dies can be held in position by the elastic force of the springs. The movable-side holder can be moved toward the stationary-side holder by drive means such as a hydraulic cylinder.
In manufacturing a bellows by means of this conventional apparatus, those portions of a cylindrical metal material which are supposed to be formed into pleats of the bellows are bulged outward by applying a bulging liquid pressure to the inside of the metal material. By operating the drive means in this state, the moveable-side holder and the dies are moved toward the stationary-side holder while maintaining a fixed liquid pressure. By doing this, the portions for the pleats of the bellows are plastically deformed to be U-shaped at a stroke. Thus, the bellows of a pre-determined shape can be obtained.
The conventional apparatus described above requires use of the dies as many as the pleats of the bellows and a large number of return springs. Besides, all the dies must slide smoothly along the guide means, so that the proximal portion of each die to engage the guide means must be made somewhat thick. If the dies are too thin, moreover, an excessive surface pressure acts on the engaging portions between the dies and the quide means when the bulging liquid pressure is applied. Naturally, therefore, the dies cannot be unlimitedly thinned, and spaces to house the return springs must be secured between the dies. Furthermore, it is difficult to regulate the pitches between the dies accurately.
For these reasons, the distance between the dies cannot be shortened without substantial restrictions, so that it is difficult to manufacture bellows with short pleat-to-pleat pitches. Since the conventional dies can be used to manufacture bellows of one specific type only, moreover, additional dies must be used to manufacture bellows with different pleat-to-pleat pitches or outside diameters, thus entailing very high manufacturing costs.